Rotatable tools such as milling cutters are equipped with a few to a large number of milling inserts. For instance, shank-end mills often include only two milling inserts, while certain types of face mills may include hundreds of milling inserts or more. A general aim in the technology in question is to design the milling tools with the smallest possible tooth pitch with the purpose of providing the same with as large a number of active cutting edges as possible, all for the purpose of minimizing the cutting forces, in particular the tangential forces, acting on the milling inserts. However, the physical nature of the milling cutter limits how close to each other the milling inserts can be mounted along the periphery of the basic body, because the tool requires a chip space or chip pocket in the area in front of the milling insert as viewed in the direction of rotation, as well as a fairly thick material portion behind the same in order to support the milling insert and carry the tangential forces.
Furthermore, all active cutting edges of the different milling inserts are usually identical in respect of the design thereof along the cutting edge lines. If the milling cutter is intended for rough milling, when considerable cutting forces arise, the cutting edges are extra strong, e.g., by the fact that one or more reinforcement bevels are formed in the same. However, if the milling cutter is to be used for fine milling and the cutting forces are moderate or small, all cutting edges are sharper or keener. Usually, the cutting edges of fine milling inserts include only a rounding, which is brushed or provided in another way, between the chip surface and the clearance surface. In some milling cutters, rough milling inserts are combined with fine milling inserts, e.g., by the fact that every second milling insert is of the first type and the other one of the second type.
In order to increase the number of active cutting edges without making it necessary to increase the number of cutting inserts and seatings in milling bodies, JP 5116018 A discloses designing the individual cutting insert with two cutting edges located behind each other. A disadvantage of the problem solution presented in the above-mentioned document is, however, that the radial distance of the rearward second cutting edge from the center axis of the individual cutting insert is greater than the one of the first front cutting edge. This means that the cutting inserts—for simple geometric reasons—have to be mounted with negative tipping-in angles in the basic body of the milling cutter. The detrimental result of this necessity is that the cutting inserts become dull-cutting.